1. Field of the Invention
The present invention is related to a novel method of producing an ether compound and to a novel polyvinyl ether compound. More particularly, the present invention is related to a method of efficiently producing a useful ether compound having a wide range of applications as solvent, lubricating oil and the like by hydrogenation of an acetal compound or a ketal compound and a novel polyvinyl ether compound useful as lubricating oil for compression-type refrigerators, electric insulation oil, organic solvent, surface active agent and the like.
2. Description of the Related Arts
As the method of producing an ether compound from acetal compounds or ketal compounds, for example, a method of using a combination of an acid and an alkali metal hydride, a method of using a silicon reagent and a method of using diborane or the like are shown in "Jikken Kagaku Koza", Volume 20, the 4th edition (published by Maruzen). However, these reactions use stoichiometric amounts of very expensive materials like the alkali metal hydride, diborane and the silicon reagent as the hydrogenating reagent and are not preferable as the method of industrial production.
A method of a combination of an acid catalyst and catalytic hydrogenation is known. W. L. Howard [J. Org. Chem. Volume 26, Page 1026 (1961)] reported formation of an ether by catalytic hydrocracking of a ketal by using a catalyst in which rhodium is supported on alumina in the presence of hydrochloric acid. In the specification of the U.S. Pat. No. 4,088,700, a method of production of an ether compound by catalytic hydrocracking of 1,3-dioxoranes which are cyclic acetals by using a platinum catalyst or a rhodium catalyst in the presence of a Lewis acid such as boron trifluoride, aluminum trichloride and the like is shown. However, because these methods of production use hydrochloric acid, boron trifluoride, aluminum trichloride and the like, corrosion of the apparatus becomes the problem when the ordinary apparatus is used and a special treatment is necessary, making the method unfavorable.
As the method without using acids, for example, methods of producing an ether compound by hydrocracking of acetals by a palladium catalyst supported on carbon were proposed in Japanese Patent Application Laid Open No. 1983-4739 and Japanese Patent Application Laid Open No. 1983-177929. Though these methods do not have the problem of corrosion of apparatus because they do not use acids, conversion of the material acetal is not satisfactory. In these methods, a processes for separating the product and the materials from each other and recycling the materials is necessary and this is not preferable. Furthermore, when the ether formed cannot be separated and purified by distillation or the like, the acetal is left in the product. Because acetals in general are lacking in stability, particularly in resistance to hydrolysis, aldehydes formed from them have oxidation, reduction, polycondensation and the like reactions to cause problem of deterioration of properties of the product to a great extent. Thus, the range of application of these methods is inevitably very limited.
Thus, a method of production of the ether compound from an acetal compound or a ketal compound which has sufficient reaction activity, shows good selectivity and does not cause corrosion of the apparatus has not been discovered yet and development of such a method is strongly desired.
Compression-type refrigerators are generally constituted with a compressor, a condenser, an expansion valve and an evaporator and has a structure that mixed fluid of refrigerant and lubricating oil is circulated in this closed system. In the compression-type refrigerator, generally temperature is 50.degree. C. or higher in the compressor and about -40.degree. C. or lower in the refrigerating chamber although the temperature is defferent depending on kind of apparatus and it is generally required that the refrigerant and the lubricating oil are circulated in the system without causing phase separation in the range of temperature of -40.degree. C. to +50.degree. C. When the phase separation occurs during the operation of the refrigerator, life and efficiency of the apparatus are adversely affected to a great extent. For example, when the phase separation of the refrigerant and the lubricating oil occurs in the part of the compressor, lubrication of the moving parts is deteriorated and seizure occurs to cause decrease of life of the apparatus to a great extent. When the phase separation occurs in the evaporator, efficiency of heat exchange is decreased because of the presence of lubricating oil of high viscosity.
Because the lubricating oil for refrigerators is used for the purpose of lubricating moving parts in refrigerators, the lubricating property is naturally important. Particularly, because the temperature in the compressor is high, the viscosity which can hold the oil film necessary for the lubrication is important. The required viscosity is different depending on the kind of the compressor used and conditions of use and it is generally preferable that viscosity (kinematic viscosity) of the lubricating oil before mixing with the refrigerant is 5 to 1000 cSt at 40.degree. C. When the viscosity is lower than this range, oil film becomes thin to cause insufficient lubrication, and, when the viscosity is higher than this range, the efficiency of the heat exchange is decreased.
Electric refrigerators have the motor and the compressor built into a single body and lubricating oil for them is required to have a high degree of electric insulating property. In general, a volume specific resistance of 10.sup.12 .OMEGA..multidot.cm or more at 80.degree. C. is required. When the resistance is lower than this value, possibility of leak of electricity arises.
As the refrigerant for compressor-type refrigerators, mainly dichlorodifluoromethane (referred to as Flon 12 hereinafter) has heretofore been used and, as the lubricating oil, various kinds of mineral oil and synthetic oil satisfying the required properties described above have been used. However, chlorofluorocarbons (CFC) including Flon 12 are being more rigorously restricted world-wide because they cause environmental pollution such as the rupture of the ozone layer. By this reason, hydrogen-containing Flon compounds such as hydrofluorocarbons (HFC) and hydrochlorofluorocarbons (HCFC) are attracting attention as the novel kinds of the refrigerant. The term Flon compound described above and hereinafter stands for a chlorofluorocarbon, a hydrofluorocarbon and a hydrochlorofluorocarbon in general. The hydrogen-containing fluorocarbons, particularly hydrofluorocarbons (HFC) represented by 1,1,1,2-tetrafluoroethane (referred to as Flon 134a hereinafter), are preferred as the refrigerant for compression-type refrigerators because they have little possibility of causing the rupture of the ozone layer and can replace Flon 12 with little change of the structure of refrigerators which have heretofore been used.
When a hydrogen-containing Flon compound described above, such as Flon 134a and the like, is adopted as the refrigerant for compression-type refrigerators to replace Flon 12, a lubricating oil having good compatibility with the hydrogen-containing Flon compound, such as Flon 134a and the like, and good lubricating property satisfying the requirements described above is naturally required. However, because the lubricating oils used in combination with Flon 12 heretofore do not have good compatibility with the hydrogen-containing Flon, such as Flon 134a and the like, a new lubricating oil suited for these compounds is required. When a new lubricating oil is adopted in accordance with replacement of Flon 12, it is desired that major change of the structure of the apparatus is not necessary. It is not desirable that the structure of the currently used apparatus must have major changes because of a lubricating oil.
As the lubricating oil having the compatibility with Flon 134a, for example, lubricating oils of polyoxyalkylene glycols have been known. For example, Research Disclosure No. 17463 (October, 1978), the specification of the U.S. Pat. No. 4,755,316, Japanese Patent Application Laid Open No. 1989-256594, Japanese Patent Application Laid Open No. 1989-259093, Japanese Patent Application Laid Open No. 1989-259094, Japanese Patent Application Laid Open No. 1989-271491, Japanese Patent Application Laid Open No. 1990-43290, Japanese Patent Application Laid Open No. 1990-84491, Japanese Patent Applications Laid Open No. 1990-132176 to 132178, Japanese Patent Application Laid Open No. 1990-132179, Japanese Patent Application Laid Open No. 1990-173195, Japanese Patent Applications Laid Open No. 1990-180986 to 180987, Japanese Patent Applications Laid Open No. 1990-182780 to 182781, Japanese Patent Application Laid Open No. 1990-242888, Japanese Patent Application Laid Open No. 1990-258895, Japanese Patent Application Laid Open No. 1990-269195, Japanese Patent Application Laid Open No. 1990-272097, Japanese Patent Application Laid Open No. 1990-305893, Japanese Patent Application Laid Open No. 1991-28296, Japanese Patent Application Laid Open No. 1991-33193, Japanese Patent Applications Laid Open No. 1991-103496 to 103497, Japanese Patent Application Laid Open No. 1991-50297, Japanese Patent Application Laid Open No. 1991-52995, Japanese Patent Applications Laid Open No. 1991-70794 to 70795, Japanese Patent Application Laid Open No. 1991-79696, Japanese Patent Application Laid Open No. 1991-106992, Japanese Patent Application Laid Open No. 1991-109492, Japanese Patent Application Laid Open No. 1991-121195, Japanese Patent Application Laid Open No. 1991-205492, Japanese Patent Application Laid Open No. 1991-231992, Japanese Patent Application Laid Open No. 1991-231994, Japanese Patent Application Laid Open No. 1992-15295, Japanese Patent Application Laid Open No. 1992-39394 and Japanese Patent Applications Laid Open No. 1992-41591 to 41592 disclosed such lubricating oils. However, the lubricating oils of polyoxyalkylene glycols generally have low volume specific resistances and no example satisfying the value of 10.sup.12 .OMEGA..multidot.cm or more at 80.degree. C. has been disclosed yet.
As the compound having the compatibility with Flon 134a in addition to the lubricating oils of polyoxyalkylene glycols, lubricating oils of esters were disclosed in British Patent Laid Open No. 2216541, WO No. 6979 (1990), Japanese Patent Applications Laid Open No. 1990-276894, Japanese Patent Applications Laid Open No. 1991-128992, Japanese Patent Applications Laid Open No. 1991-88892, Japanese Patent Applications Laid Open No. 1991-179091, Japanese Patent Applications Laid Open No. 1991-252497, Japanese Patent Applications Laid Open No. 1991-275799, Japanese Patent Applications Laid Open No. 1992-4294, Japanese Patent Applications Laid Open No. 1992-20597 and the specification of the U.S. Pat. No. 5,021,179. However, it is inevitable because of the structural characteristic that carboxylic acids are formed by hydrolysis of the lubricating oils of esters.
Lubricating oils of carbonates were disclosed in Japanese Patent Application Laid Open No. 1991-149295, European Patent No. 421298, Japanese Patent Application Laid Open No. 1991-217495, Japanese Patent Application Laid Open No. 1991-247695, Japanese Patent Application Laid Open No. 1992-18490 and Japanese Patent Application Laid Open No. 1992-63893. However, the lubricating oils of carbonates have the same problem of hydrolysis as the lubricating oils of esters.
Thus, it is the real situation at present that a lubricating oil for the compression-type refrigerators having excellent compatibility with Flon 134a, excellent stability and lubricating property and a volume specific resistance at 80.degree. C. of 10.sup.12 .OMEGA..multidot.cm or more has not been discovered yet. Development of such a lubricant is strongly desired.
Concerning generally known polyalkyl vinyl ethers, examples of synthesis of various kinds of alkyl polyvinyl ether are described in "Jikken Kagaku Koza", Volume 18, "Reaction of organic compounds II(A)", edited by Chemical Society of Japan (published by Maruzen). Ends of these polymers are olefins in the case of the acid catalysts and acetals when an alcohol is present in addition to the acid catalyst. When water is present, ends of acetal and ends of aldehyde are also formed. The end of olefin causes coloring and increase of viscosity in the presence of an acid and the end of aldehyde also causes coloring. Acetals are decomposed to olefins and alcohols in the presence of an acid. The olefins react with each other to cause coloring and increase of viscosity and, when water is present additionally, aldehydes are formed, also causing coloring. However, a polyvinyl ether compound which does not contain these structures causing degradation, such as the structures of acetals, aldehydes and olefins, at the end of the molecule has not been reported yet.